The invention relates broadly to tire building machinery, and specifically to a device that is used in connection with a tire building drum to turn-up the ply endings, of an unvulcanized tire carcass, around the tire beads to anchor the beads firmly to the tire carcass of a truck, passenger, or off-the-road tire.
An unvulcanized tire carcass is built by an operator who layers on a rotary tire building drum, one or more plies of tire cord fabric that has been calendered with unvulcanized rubber material. The unvulcanized tire carcass is then secured between a pair of parallel tire beads which are, normally, inextensible wire rings that are used to mount the finished, vulcanized tire on a wheel rim. The securement of the two bead rings to the unvulcanized tire carcass is made by first positioning the bead rings around the tire carcass inwardly of the opposing ends of the tire carcass, so that the endings of the carcass ply or plies extend outwardly beyond the bead rings. These ply endings are then turned up and reversely wrapped around the bead rings and pressed or stitched against the carcass ply or plies to firmly lock the bead rings to the unvulcanized tire carcass. The turn-up of the ply endings is accomplished by the use of a pair of annularly shaped rubber bladders which are positioned adjacent opposing ends of the drum and which are inflated with air to expand and engage the ply endings and roll them over the bead rings into compressive engagement with the portions of the tire carcass immediately inwardly of the bead rings. This turn-up process, carried out primarily by the turn-up bladders, is critical to the building of a good tire, and care must be taken to avoid the formation of voids during the process, since voids trap within the structure of the tire, air which adversely affects the adhesion between the bead rings and surrounding rubber material. This condition causes the beads to separate from the surrounding rubber material during operation of the tire as it rapidly rotates and bounces along a highway. This damage to a tire cannot be repaired, and a tire, so damaged, must be discarded and replaced.
U.S. Pat. No. 4,087,306 describes some of the problems encountered in controlling the inflation and corresponding movement of the turn-up bladders to make a good tight wrapping of the bead rings with the ply endings. The invention of U.S. Pat. No. 4,087,306 mainly concerned with controlling the rollover motion of the turn-up bladders, after the bladders move initially, which initial movement is difficult to predict and control. FIG. 8 of U.S. Pat. No. 4,087,306 shows that the inboard portion of each bladder, i.e. the part of the bladder closest the tire building surface of the drum, expands inside the bead rings closest the longitudinal center axis of the drum. It can be appreciated that, any movement of this inboard portion of the bladder inwardly of the drum, can cause adjacent the insides of the bead rings, a slackening or bunching of the carcass ply or plies which, in turn, can produce voids in these critical areas of the tire. U.S. Pat. No. 4,087,306 also discloses a turn-up bladder which is designed for interlocking engagement with a number of bead lock segments which are movable in radial directions, relative to the center axis of the drum, to grasp and hold the bead rings firmly in position while the ply endings are turned up around the bead rings. Initial movement of these bladders inwardly of the drum could cause similar problems. Thus, the sole use and reliance upon air bladders to effect a good turn-up of the ply endings is doubtful.
U.S. Pat. No. 4,007,081 discloses the use of an elastic drum sleeve for tensioning the carcass ply or plies between the bead lock segments. This is important in making a good, tight wrapping of the bead rings, but even more essential is the tensioning of the ply endings for which this patent apparently relies on the expansion of the turn-up bladders. Thus, in the respect U.S. Pat. No. 4,007,081 is similar in scope of the aforementioned U.S. Pat. No. 4,087,306.
The invention of this application is directed to maintaining the ply endings of the carcass ply or plies in tension during the turn-up process, as a means of forming a tight as wrap as possible to eliminate the formation of voids adjacent the bead rings.
Briefly stated, the invention is in a tire building drum that has an outer cylindrical shell, a plurality of radially movable bead lock segments adjacent each of the opposing ends of the shell, and a generally annularly shaped, inflatable turn-up bladder which is disposed outwardly of each group of bead lock segments. A pair of special carriers cover the exposed faces of the bead lock segments and at least partially surround the adjacent turn-up bladder. Each of the carriers is composed of a material which is inextensible in a direction longitudinally of the drum. The carrier has an inboard end which is secured inwardly of the bead lock segments and an outboard end which is secured outwardly of the bead lock segments. Each carrier is of a length to snugly fit the adjacent turn-up bladder, so that, upon radial expansion or movement of the bead lock segments, the material of the carriers will be tensioned to distort the shape of the turn-up bladders which will react to this imposition by the carriers to maintain constant tension on the carriers which, in turn, tension the ply endings, especially during the initial stages of the turn-up process.
In certain designs of the bead lock segments, the carcass ply or plies between the bead lock segments will also be stretched and tensioned upon radial expansion or movement of the bead lock segments.